A drop cable is used as the last link in a cable TV system to bring the cable TV signal from a trunk line, passing near the subscriber's home, directly into the subscriber's home. Typically the drop cable is either buried underground, or run aerially into the subscriber's home. The drop cable is a coaxial cable design typically including a center conductor, a surrounding dielectric, an outer conductor, and an overall protective plastic jacket.
The outer conductor of a conventional drop cable is typically provided by a foil shield and a covering of wires thereover. The covering is often in the form of a braid provided by a plurality of relatively small diameter round wires which permit the cable to retain a high degree of flexibility, yet which reinforce the foil shield.
Attempts have been made in the prior art to improve various components of the drop cable. For example, U.S. Pat. No. 4,691,081 to Gupta et al., and assigned to the assignee of the present invention, discloses a drop cable having an improved foil shield comprising a metal foil layer and a polymer supporting layer fusibly bonded directly to the foil shield layer and serving to structurally reinforce the foil shield layer. U.S. Pat. No. 4,701,575 to Gupta et al. discloses a corrosion-inhibiting powder disposed between the outer conductor comprising a foil shield and braided reinforcing covering and the outer protective plastic jacket.
Unfortunately, it has been found during the manufacture of conventional drop cables, that the relatively small diameter round wires forming a typical braided covering will easily break unless the braiding is done at a relatively slow speed. For example, the braiding operation may typically be performed at a rate of only about 10 to 11 linear feet per minute. In contrast, the final step of applying the protective plastic jacket can be performed at speeds as high as 450 linear feet per minute. Moreover, proper extrusion of the plastic jacket requires a higher linear speed than 10 to 11 feet per minute. Thus, two discrete process steps are required to form the braid and then apply the outer protective plastic jacket in a conventional drop cable manufacturing process.
The cost of the raw material for making a coaxial drop cable is often an important factor in the cable design. For a cable television company having thousands of miles of drop cable, the cost savings of a minor reduction in the amount of material in the drop cable becomes significant. Unfortunately, it is not possible to reduce the amount of metal in the round reinforcing wire covering of the prior art drop cable without compromising the strength of the cable or without further reducing the speed of the braiding step.
It may also be desirable to increase the percentage of coverage that the reinforcing layer provides to the electrically conductive foil shield to thereby reduce leakage of the high frequency of signals from the cable. In a conventional round wire reinforcing covering, an increase in the desired coverage would require a greater quantity of metal and, therefore, add to the overall expense of the cable.